It is known to replace diseased or damaged articulating surfaces of a joint with prosthetic components in total or partial joint replacement procedures. During such procedures, damaged bone tissue is cut away, leaving clean resected bone surfaces for attachment of prosthetic components. Correct positioning of the resected surfaces is vital to ensuring correct balancing of soft tissues and transfer of forces through the reconstructed joint. Guide tools are conventionally employed to direct the correct positioning of bone cuts with reference to patient anatomy. For example, in a total ankle replacement procedure, it is considered desirable to resect the distal tibia along a plane that is perpendicular to the longitudinal axis of the tibia. Guide tools are known that align with the long axis of the tibia and present a guide surface that is perpendicular to this long axis, thus directing perpendicular resection of the distal tibia. There are circumstances however when alignment with reference to conventional physical features can be difficult and/or disadvantageous. For example, for patients with a bowed or otherwise abnormal tibia, resection of the distal tibia with reference to the tibial long axis can be difficult to achieve, and may result in less than optimal transmission of forces through the joint.